A large diameter pipeline that is used to convey fluid products such as crude oil, water or gas over long distances, for example between an oil field and a refinery or another pipeline, must occasionally be tested to confirm that there are no leaks in the line which could pose a hazard to the environment or to individuals or property along the route. Testing also must be performed on all new or pre-commissioned lines, as well as after a leak has been located and repaired in an operational pipeline. To test a pipeline, a procedure generally known as hydrotesting can be used which involves replacement of the product in the line with water, pressurizing the water to a predetermined value, and monitoring the pressure and temperature of the water in the line to determine if there are any leaks. Although a test of an entire pipeline conceivably could be accomplished in a single operation, it is more typical for a series of independent tests to be made of relatively short-length segments thereof. This is because a pipeline, which may be many hundreds or even thousands of miles long, usually is divided into segments that have mainline valves at each end. These valves may be anywhere from a few miles to hundreds of miles apart. Since testing involves temporary shut-down of the pipeline, which adversely impacts the operation of those refineries and other facilities which depend upon its throughput, there is a compelling need to conduct hydrotesting operations as quickly, reliably and economically as possible.
To conduct a meaningful hydrotest of a pipeline segment, there must be assurance that the test segment is positively isolated. If the valves that are used to isolate the test segment leak during the test, it is not possible to determine from water pressure and temperature data whether the pipeline segment itself will hold pressure or not. Therefore some means should be provided to positively seal off these valves during the test so that if the test pressure drops off, the leak must be somewhere in the segment. In the past, one process that has been used involves cutting the pipeline and installing test headers to isolate the mainline valves during testing. This procedure is very labor intensive and costly, takes a considerable amount of time, and is destructive to the pipeline. Another technique that has been tried is to form ice plugs adjacent the mainline valves by freezing. However, this technique is not particularly feasible for use in connection with a large diameter pipeline. Thus the problem of providing a quickly implemented, economical and reliable way to positively seal off a mainline, a branch line or a cross-over valve during a hydrotest of a pipeline segment remains unsolved.
An object of the present invention is to provide new and improved methods and apparatus for positively sealing off a mainline or other valve in a pipeline which obviates the foregoing problems and difficulties with prior schemes.
Another object of the present invention is to provide new and improved methods and apparatus of the type described where a gel mixture that can be easily injected into, and removed from, an inner region of a pipeline adjacent a mainline valve is used to positively seal off the valve during a hydrotest.
Still another object of the present invention is to provide new and improved methods and apparatus of the type described where an aqueous-based highly viscous gel having a lost-circulation material suspended therein is injected into the pipeline adjacent a mainline or similar valve which bridges over and seals off any leakage paths in the valve so that a segment of a pipeline having the valve therein can be hydrotested.